BiFET Bias Circuit for RF Amplifiers Without Reference Voltage Drop
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Solution Overview
Problem
Conventional bias circuits for RF power amplifiers are affected by voltage drops across transistor switches, leading to actual reference voltages that may be out of specification, impacting performance.
Innovation Solution
A bias circuit using a BiFET process with a field-effect transistor controlled by a logic signal to supply bias current to an RF power amplifier, integrating bipolar and field-effect transistors on a single-chip integrated circuit, ensuring the reference voltage is not affected by the transistor switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a transistor switch is used in the conductive path from reference voltage to bias circuit for controlling bias current, then the bias current can be controlled to be supplied or not supplied to the power amplifier, but the voltage drop across the transistor switch causes the actual reference voltage to be out of specification
Solution Approach 1:
A dedicated voltage buffer stage is introduced as an intermediary component between the reference voltage source and the bias circuit. This buffer stage isolates the reference voltage from voltage drops in the transistor switch and conductive path, ensuring that the actual reference voltage remains within specification regardless of the switch state or current variations in the bias circuit.
Solution Approach 2:
The circuit is segmented into distinct functional blocks: a reference voltage source, a voltage buffer stage, a transistor switch for current control, and a bias circuit. By separating the voltage reference function from the current control function, the design ensures that voltage accuracy is maintained independently of the switching operation.
2Adaptability or versatility
If a transistor switch is placed in the conductive path to control bias current, then the power amplifier can be enabled or disabled, but the voltage drop across the switch affects the reference voltage stability
Solution Approach 1:
The voltage buffer acts as a mediator that decouples the reference voltage from the switching operation. It provides a stable reference voltage to the bias circuit regardless of whether the transistor switch is on or off, thereby maintaining reference voltage stability while enabling power amplifier control.
Solution Approach 2:
The reference voltage is established and stabilized by the buffer stage before being used by the bias circuit. This preliminary establishment of a stable reference voltage ensures that subsequent switching operations do not compromise voltage stability.
Data Source
AI summary
A bias circuit for supplying a bias current to an RF power amplifier by using a field-effect transistor (FET) that is controlled by a logic control signal, such as a CMOS logic control signal, for turning on or turning off the bias current supplied to the RF power amplifier, wherein the bias current will be supplied to the RF power amplifier when the FET is on, and the bias current will not be supplied to the RF power amplifier when the FET is off.